When we consider
a C++ program, it can be defined as a collection of objects that communicate
via invoking each other's methods. Let us now briefly look into what a class,
object, methods, and instant variables mean.
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Object − Objects have states
and behaviors. Example: A dog has states - color, name, breed as well as
behaviors - wagging, barking, eating. An object is an instance of a class.
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Class − A class can be
defined as a template/blueprint that describes the behaviors/states that object
of its type support.
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Methods − A method is
basically a behavior. A class can contain many methods. It is in methods where
the logics are written, data is manipulated and all the actions are executed.
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Instance Variables −
Each object has its unique set of instance variables. An object's state is
created by the values assigned to these instance variables.
C++ Program Structure
Let us
look at a simple code that would print the words Hello World.
#include <iostream>
using namespace std;
// main() is where program execution begins.
int main() {
cout << "Hello World"; // prints Hello World
return 0;
}
Let us
look at the various parts of the above program −
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The C++ language defines several headers, which contain
information that is either necessary or useful to your program. For this
program, the header <iostream> is needed.
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The line using namespace std; tells the compiler
to use the std namespace. Namespaces are a relatively recent addition to C++.
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The next line '// main() is where program execution begins.'
is a single-line comment available in C++. Single-line comments begin with //
and stop at the end of the line.
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The line int main() is the main function where
program execution begins.
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The next line cout << "This is my first C++
program."; causes the message "This is my first C++
program" to be displayed on the screen.
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The next line return 0; terminates main(
)function and causes it to return the value 0 to the calling process.
Compile and Execute C++ Program
Let's
look at how to save the file, compile and run the program. Please follow the
steps given below −
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Open a text editor and add the code as above.
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Save the file as: hello.cpp
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Open a command prompt and go to the directory where you saved the
file.
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Type 'g++ hello.cpp' and press enter to compile your code. If
there are no errors in your code the command prompt will take you to the next
line and would generate a.out executable file.
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Now, type 'a.out' to run your program.
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You will be able to see ' Hello World ' printed on the window